The long range objective of this project is to study the mechanism of expression of endogenous viral genes by normal physiological stimuli. In particular, we are concerned with xenotropic viruses and possible host cell modification of viral protein and nucleic acid composition. Present studies include: (1) Characterization of DNA found in type C virions and determination of possible functions, e.g., transfer of cellular information among cells or carrying pathogenic information. (2) Examination of the mechanism of high incidence of adrenal carcinoma and lymphoma in aged NIH Swiss mice which were ovariectomized prior to sexual maturity. (3) Determination of tRNA primer for cDNA synthesis from high molecular weight viral RNA of NIH Swiss virus M55. BIBLIOGRAPHIC REFERENCES: Strickland, J. E., Saviolakis, G. A., Folwer, A. K., Kouttab, N. M., and Hellman, A.: Impaired estrogen-mediated production of type C viral DNA polymerase in aged NIH Swiss mouse uteri. Proc. Soc. Exp. Biol. Med. 153: 63-69, 1976. Fowler, A. K., Strickland, J. E., Kouttab, N. M., and Hellman, A.: RNA tumor virus expression in mouse uterine tissue during pregnancy. Biol. Reprod. 16: 344-348, 1977.